Embodiments herein generally relate to structures and methods that help remove oil from percolation paths and more particularly to a structure and method that applies interference of sound waves from one or more sources to control the locations where solids separate from liquids.
It has been estimated that only half of the oil present in a natural reservoir is produced by primary, secondary, and tertiary oil recovery techniques combined. This is due to the formation of percolation paths in which injected gases or fluids break through to adjoining (extraction) boreholes. Once this happens no new oil is forced out because all injected fluids follow the established percolation paths to the extraction boreholes.
In one embodiment herein a method comprises controlling a plurality of sonic sources to generate sound waves within at least one borehole opening in the ground. A percolation path is one that comprises a combination of liquid particles (oil) and solid particles (rocks, dirt). If one is to view rock as a porous solid, consisting of the solid rock frame containing pores, these pores typically contain fluid (water, brine, oil, gas). In some regions the pores may connect and form a continuous path through which the fluids can move if/when subjected to a pressure gradient. When fluids are injected into one borehole other fluids can be forced out of some neighboring extraction borehole. However, they don't have to be, especially in reservoirs containing gas. At any rate, the regions in which fluids are moving are called percolation paths. These moving fluids might be pore fluids originally in the reservoir (oil, gas, brine), or they might be injected fluids (water, steam, detergents, borehole mud, etc.)
The sound goes to many areas of the item (e.g., the oil reservoir). This disclosure is interested in how the second sound wave interacts with pore fluids along the periphery of the active percolation paths. In particular, the second sound should encourage migration of in-situ pore fluids from the periphery into active percolation paths.
By controlling the sonic sources, the method transmits the sound waves to the percolation path. Further, the method regulates the amplitude and frequency of the sound waves such that the liquid particles oscillate out of phase with the solid particles. The method also regulates the phases of the sound waves generated by the different sonic sources so as to control locations within the percolation path where the liquid particles oscillate out of phase with the solid particles.
Further, different embodiments herein can position the sonic sources within the borehole openings so as to form a regular pattern of the sonic sources within the ground. Embodiments herein can also maintain the sonic sources at fixed positions with the ground.
The regulating of the phases of the sound waves causes the sound waves to combine is specific locations of the percolation path and causes the sound waves to cancel each other out in other locations of the percolation path. Thus, embodiments herein can regulate the phases of the sound waves and the amplitude and frequency of the sound waves generated by different ones of the sonic sources so as to control locations within the percolation path where the liquid particles oscillate out of phase with the solid particles and to control amounts by which the liquid particles oscillate out of phase with the solid particles.
An apparatus embodiment herein includes a controller connected to a plurality of sonic sources. Each of the sonic sources comprises an external cover and at least one sonic acoustic acoustic generator. The external cover can be made of a sealed, liquid-tight, and gas-tight material that is adapted to be positioned within an opening of an item, or can be formed of any appropriate material that will be durable in the environment in which the sonic source will be located. The opening (e.g., borehole in the ground) can be fully or partially lined with a casing, or can be unlined. The item (e.g., ground) comprises at least one percolation path having a combination of liquid particles and solid particles. The sonic acoustic acoustic generator can be positioned within the borehole opening and is adapted to generate and transmit sound waves into the percolation paths.
The controller regulates the amplitude and frequency of the sound waves such that the liquid particles oscillate out of phase with the solid particles. Further, the controller is adapted to regulate the phases and amplitudes of the sound waves generated by the different sonic sources so as to control locations within the percolation path where the liquid particles oscillate out of phase with the solid particles and to control amounts by which the liquid particles oscillate out of phase with the solid particles.
In another embodiment, each of the sonic sources can include a plurality of sonic (acoustic) generators positioned within the borehole opening. The structure includes at least one support structure (cable, wire, pipe, frame, etc.) connected to the external cover. The support structure is adapted to maintain at least one of the sonic sources at a fixed position with the borehole opening.
Primary oil recovery uses the natural pressure of the oil reservoir to push oil to the surface. In secondary oil recovery gases or water is forced into the reservoir to force oil out through adjacent boreholes. In tertiary recovery other gases (such as carbon dioxide), or heat (steam or hot water) are used to stimulate oil and gas flow to produce remaining fluids that were not extracted during primary or secondary recovery phases. The amount of fluid forced into one well equals roughly the amount of fluid withdrawn from another well, hopefully oil. This is true in regions where the pore fluid is incompressible, e.g., oil, brine. It is not always true in regions where the pore fluid is compressible, e.g., gas. Typically, oil recovery techniques cease to be useful when a percolation path for the injected fluid or gas breaks through from the insertion well to the withdrawal well. Even with enhanced oil recovery techniques, only about half of the oil in a natural oil reservoir is recovered in the primary, secondary and tertiary oil recovery, leaving the rest unrecoverable. Thus, there is considerable oil value left in the ground in mature oil fields. Any new technique that will increase recovery of oil from these previously recovered reservoirs is valuable.
In June 2002 a patent (U.S. Pat. No. 6,405,796) was issued to Robert Meyer and Christine Tarnawskyj for a method of enhancing oil recovery by using ultrasonics. This patent uses ultrasonics at a specific frequency (determined by the rock permeability and fluid density and viscosity) to excite a second sound mode in which the porous rock oscillates out of phase with the fluids in the pores of the permeable rock. Thus, the rock frame moves one direction and the pore fluid moves the other way. This process is referred to as “second sound” and can be used to move oil contained in pores adjacent to an operating percolation path into the flow path. Thus, oil that might otherwise be unrecoverable is recovered. The basic physics of second sound) is well established in the scientific literature (cited in U.S. Pat. No. 6,405,796).